from __future__ import annotations
from functools import partial
import numpy as np
import gdsfactory as gf
from gdsfactory.component import Component
from gdsfactory.components.grating_coupler_elliptical import grating_tooth_points
from gdsfactory.geometry.functions import DEG2RAD
from gdsfactory.typings import CrossSectionSpec, LayerSpec
[docs]
@gf.cell
def grating_coupler_elliptical_trenches(
polarization: str = "te",
taper_length: float = 16.6,
taper_angle: float = 30.0,
trenches_extra_angle: float = 9.0,
wavelength: float = 1.53,
fiber_angle: float = 15.0,
grating_line_width: float = 0.343,
neff: float = 2.638, # tooth effective index
ncladding: float = 1.443, # cladding index
layer_trench: LayerSpec | None = "SHALLOW_ETCH",
p_start: int = 26,
n_periods: int = 30,
end_straight_length: float = 0.2,
cross_section: CrossSectionSpec = "xs_sc",
**kwargs,
) -> Component:
r"""Returns Grating coupler with defined trenches.
Some foundries define the grating coupler by a shallow etch step (trenches)
Others define the slab that they keep (see grating_coupler_elliptical)
Args:
polarization: 'te' or 'tm'.
taper_length: taper length from straight I/O.
taper_angle: grating flare angle.
wavelength: grating transmission central wavelength.
fiber_angle: fibre polish angle in degrees.
grating_line_width: of the 220 ridge.
neff: tooth effective index.
ncladding: cladding index.
layer_trench: for the trench.
p_start: first tooth.
n_periods: number of grating teeth.
end_straight_length: at the end of straight.
cross_section: cross_section spec.
kwargs: cross_section settings.
.. code::
fiber
/ / / /
/ / / /
_|-|_|-|_|-|___
WG o1 ______________|
"""
xs = gf.get_cross_section(cross_section, **kwargs)
wg_width = xs.width
layer = xs.layer
# Compute some ellipse parameters
sthc = np.sin(fiber_angle * DEG2RAD)
d = neff**2 - ncladding**2 * sthc**2
a1 = wavelength * neff / d
b1 = wavelength / np.sqrt(d)
x1 = wavelength * ncladding * sthc / d
a1 = round(a1, 3)
b1 = round(b1, 3)
x1 = round(x1, 3)
period = float(a1 + x1)
trench_line_width = period - grating_line_width
c = gf.Component()
# Make each grating line
for p in range(int(p_start), int(p_start + n_periods + 1)):
pts = grating_tooth_points(
p * a1,
p * b1,
p * x1,
width=trench_line_width,
taper_angle=taper_angle + trenches_extra_angle,
)
c.add_polygon(pts, layer_trench)
# Make the taper
p_taper = p_start - 1
p_taper_eff = p_taper
a_taper = a1 * p_taper_eff
# b_taper = b1 * p_taper_eff
x_taper = x1 * p_taper_eff
x_output = a_taper + x_taper - taper_length + grating_line_width / 2
xmax = x_output + taper_length + n_periods * period + 3
y = wg_width / 2 + np.tan(taper_angle / 2 * np.pi / 180) * xmax
pts = [
(x_output, -wg_width / 2),
(x_output, +wg_width / 2),
(xmax, +y),
(xmax + end_straight_length, +y),
(xmax + end_straight_length, -y),
(xmax, -y),
]
c.add_polygon(pts, layer)
x_output = gf.snap.snap_to_grid(x_output)
c.add_port(
name="o1",
center=(x_output, 0),
width=wg_width,
orientation=180,
layer=layer,
cross_section=xs,
)
c.info["period"] = period
c.info["polarization"] = polarization
c.info["wavelength"] = wavelength
x = np.round(taper_length + period * n_periods / 2, 3)
c.add_port(
name="o2",
center=(x, 0),
width=10,
orientation=0,
layer=layer,
port_type="optical",
)
return c
grating_coupler_te = partial(
grating_coupler_elliptical_trenches, polarization="te", taper_angle=35
)
grating_coupler_tm = partial(
grating_coupler_elliptical_trenches,
polarization="tm",
neff=1.8,
grating_line_width=0.6,
)
if __name__ == "__main__":
c = grating_coupler_te()
# c = grating_coupler_elliptical_trenches(polarization="TE")
# print(c.polarization)
# c = grating_coupler_te(end_straight_length=10)
# c = grating_coupler_tm()
# print(c.ports.keys())
# c = gf.routing.add_fiber_array(grating_coupler=grating_coupler_elliptical_trenches)
c.show(show_ports=True)
